A. Field of the Invention
This invention relates to a graphics system for three-dimensional graphic representation, which can quickly draw a shadow of an object by utilizing hidden-surface hardware implementing Z-buffer processing including, e.g. scan line Z-buffer processing, to enable the presence or absence of a shadow to be determined with a simple system arrangement.
B. Prior Art
Conventional shadow generation techniques are divided into the three techniques of shadow mapping, ray tracing and shadow polygon determination. The shadow polygon technique that will be described more fully later is a variation of the hidden-surface elimination process, and differs from the other two techniques in the fact that it can be incorporated in hardware and its processing speed can be improved by using the scan line process or the Z-buffer process. The present invention is directed to an improvement on the prior art shadow polygon process.
The original prior art shadow polygon process is described first, and then a prior art algorithm by Brotman and Badler that allows use of the shadow polygon process in combination with the Z-buffer process is described.